# Yields of weakly-bound light nuclei as a probe of the statistical hadronization model

## TL;DR

This paper investigates whether the statistical hadronization model's chemical freeze-out temperature accurately reflects the physical conditions of weakly-bound light nuclei, questioning the model's underlying assumptions.

## Contribution

The study critically examines the assumptions of the statistical hadronization model using yields of weakly-bound nuclei, revealing inconsistencies with the model's core premises.

## Key findings

- Weakly-bound nuclei yields challenge the assumption of thermal equilibrium at freeze-out.
- The chemical freeze-out temperature may not represent the actual physical temperature for these nuclei.
- The model's assumption of an ideal gas of hadrons and nuclei is inconsistent with the observed yields.

## Abstract

The statistical hadronization model is a simple and efficient phenomenological framework in which the relative yields for very high energy heavy ion collisions are essentially determined by a single model parameter---the chemical freeze-out temperature. Recent measurements of yields of hadrons and light nuclei covering over 9 orders of magnitudes from the ALICE collaboration at the LHC were described by the model with remarkable accuracy with a chemical freeze-out temperature of 156.5 $\pm$ 1.5 MeV. A key physical question is whether the freeze-out temperature can be understood, literally, as the temperature at which the various species of an equilibrated gas of hadrons (including resonances) and nuclei chemically freeze out as the model assumes, or whether it successfully parametrizes the yield data for a different reason. The yields of weakly-bound light nuclei---the deuteron and the hypertriton---provide insights into this issue. The analysis indicates that a key assumption underlying the model---that hadrons (and nuclei), just prior to chemical freeze-out temperature, are in thermal equilibrium and are sufficiently dilute as to have particle distributions accurately described statistically by a nearly ideal gas of hadrons and nuclei with masses given by their free space values---appears to be inconsistent with the chemical freeze-out temperature output by the model, at least for these weakly-bound nuclei.